1. Field of the Invention
The invention relates to an operation control apparatus for a power converter (power conditioner) in a solar power system.
2. Description of the Related Art
Patent Literature 1 discloses, as capability to effectively use generated power of a solar battery, an invention which suppresses a voltage rise at a power reception point connected to a power converter and to a power system, by making an ineffective phase advance current constantly flow while maintaining an effective current output.
Patent Literature 2 describes that an upper limit and a lower limit are provided for a link point in order that an output power of a dispersed power supply which is operated in cooperation with a power system is restricted from greatly hunting to maintain a constant link point voltage. When the link point voltage is within the limits, the link point voltage is restricted to be not greater than the upper limit, by continuing both controls (Normally, operation is performed to output the maximum power at a power ratio of 100%. Only when the link point voltage exceeds a limit, an effective power and an ineffective phase advance voltage are controlled to restrict the link point voltage). Only when the link point voltage is not greater than the lower limit, normal operation is recovered in which the maximum power at the power ratio of 100% is output.
Conventionally, there is a problem as follows in a system which converts direct-current power generated from a solar battery into alternating-current power by a power converter (power conditioner) and supplies the power to an alternating-current power system. In the power converter, power conversion is not performed unless a direct-current voltage from a solar power generation apparatus exceeds a minimum value (lower limit) when an alternating-current voltage is supplied to an alternating-current power system. The minimum value (lower limit) in this case is a value which is marginally tolerable. However, since voltage fluctuation occurs on the alternating-current side, effective use of the generated power from the solar battery is not achieved.
When the direct-current voltage which is an input voltage of the power converter exceeds the minimum value (lower limit), the power converter is operated but the minimum value (lower limit) of the direct-current voltage is still fixed. Here, the minimum value (lower limit) of the direct-current voltage is determined to be the value when the solar power generation apparatus is under the worst conditions.